Best Audio Settings?

I was wondering about the best Audio Settings to use. The settings have either PCM or Default (Stereo).
I have a 5.1 channel surround system that is capable of Dolby Digital. I love my sound, and was wondering what is the best profile to use in Videostream? I am not an expert in these things, so I am asking so I can utilize the best of what I have.

Does Videostream support 5.1 surround sound profiles in mp4/mkv files?